Microsoft's own field rep is poaching my CSP customer with $500K in incentives... anyone fought back and won?

hey guys, hoping i can get some help :( I have a customer up for renewal, decent-sized deal. Out of nowhere, their Microsoft account executive who was supposed to be helping them navigate their tech stack is now pitching them to sign directly with Microsoft and dangling over $500K in ease of funds to make it happen. This is a customer I've been managing for years. I have GDAP access, I know their environment, I've been their go-to for licensing and support. And now the Microsoft rep who was supposed to be a resource is essentially working against me. I've already reached out to my PDM and I'm getting in front of the customer this week to walk them through what they'd actually be giving up. Curious if anyone has successfully pushed back on this kind of situation, whether there's a formal Microsoft partner complaint process that actually does anything?? Feels like Microsoft is increasingly comfortable stepping on partners when the deal is big enough. Would love to hear if others have been through this and what actually worked. I feel so frustrated and powerless.